Heating with Thermal Storage and Low Flow Temps
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Just thought I would put the above in context via wood usage. I just got back from a 4 day business trip so I got to see exactly how much wood my wife used. The last fire I started was Monday night, my wife did all the burning Tuesday - Fri night, I started a fire this AM. I have 2 4x4 racks in the basement and she used about 1.5 racks worth with at least 25% being pine. This was the coldest week we have had this year, in the teens every night and I do not believe it ever got out of the 20's during the day. Curious how this compares to others usage (understanding it depends on sq ft, how hot you keep the house, etc.).
Tom C - I know you log your wood usage, what are your thoughts?
Somewhere, maybe a different thread, we talked about the value of dry wood and the problems associated with bridging. Last year was a moist wood, bridging nightmare, Went on the same trip last year and my wife burned 2x the wood. I attribute most of the difference in the wet wood and bridging that came from it but am please at how little wood was needed.
Tom C - I know you log your wood usage, what are your thoughts?
Somewhere, maybe a different thread, we talked about the value of dry wood and the problems associated with bridging. Last year was a moist wood, bridging nightmare, Went on the same trip last year and my wife burned 2x the wood. I attribute most of the difference in the wet wood and bridging that came from it but am please at how little wood was needed.
maple1
Minister of Fire
How long is your wood?
I measured the useable space in my firebox a couple years ago & came up with 3 cu.ft.. I don't use all that space, as it is about 22" deep and I aim to cut my wood at 18". Some rough figuring on 2 loads a day comes up with about 5 cu.ft./day for this time of year. Give or take, ballpark like.
(It was -18c here when I got up this morning - but calm & clear, thankfully. Should be good solar gain today once the sun gets up, going out later & wont be back to light up until 7pm or so maybe...)
I measured the useable space in my firebox a couple years ago & came up with 3 cu.ft.. I don't use all that space, as it is about 22" deep and I aim to cut my wood at 18". Some rough figuring on 2 loads a day comes up with about 5 cu.ft./day for this time of year. Give or take, ballpark like.
(It was -18c here when I got up this morning - but calm & clear, thankfully. Should be good solar gain today once the sun gets up, going out later & wont be back to light up until 7pm or so maybe...)
I shoot for 18" when I cut it but I get a lot of precut stuff. I would guess average of 15" this year.
If my memory is working my firebox holds 195 liters (from the specs). If I had to guess I would say a load usually is only 80% of this.
velvetfoot
Minister of Fire
Armaton
Member
maple1
Minister of Fire
So using 4x4, x1.5, x16", over 4 days, I come up with 8 cu.ft. per day?
(Roughly speaking...)
Sounds reasonable but I have nothing to compare it to - is that good, bad, normal? I know it is a lot better than last year
Yu probably mentioned it before, how many sqft are you heating and what temp do you heat the house to? Just trying to get something to compare, understanding that it is impossible to get apples to apples.
maple1
Minister of Fire
20 year old 2700 sq.ft on 2 storeys, over 1500 sq.ft. of unfinished unheated basement. On an open hilltop. It doesn't do bad but there's room for improvement. Our siding is starting to look a little dated, if that ever gets redone there will be a layer of foam board under the new stuff. Really notice a heatload difference when its windy out.
I setback 3°c during the day in zones that aren't being used. And overnight also I guess on the opposite zones. Otherwise stats are at 20c, except for living room zone that is set at 22c in the evenings when everyone is in it and just sitting still. If its extra cold out, I'll set the others up 1 degree higher while I'm burning, sort of acts like having more storage. Aside from running storage as low as I can, I think timing burns with max heat demand helps too. So I am doing the bulk of my setback recovery late afternoon, just about the same time as my boiler is getting a good head of steam up.
I setback 3°c during the day in zones that aren't being used. And overnight also I guess on the opposite zones. Otherwise stats are at 20c, except for living room zone that is set at 22c in the evenings when everyone is in it and just sitting still. If its extra cold out, I'll set the others up 1 degree higher while I'm burning, sort of acts like having more storage. Aside from running storage as low as I can, I think timing burns with max heat demand helps too. So I am doing the bulk of my setback recovery late afternoon, just about the same time as my boiler is getting a good head of steam up.
Thanks for the info, there are a million variables but having an idea of what others are doing helps create some type of Benchmark.
maple1
Minister of Fire
That's about 6 cu.ft. if I did my math right. Or twice the volume of what I measured mine to be. I think I'll double check my measurements when I clean tomorrow.
It is actually 195 liters (per the literature), using an online conversion tool that = 6.88 cuft. Thinking about the guesstimate on 8 cuft per day (on avg) with approx 75 - 80% loaded - works out to about 6 fires. This sounds about right based on when I think my wife started fires over the last 4 days. We fill the firebox as much as we can but based on reality. shorter pieces of wood, space between wood, etc. 75 - 80% sounds about right to me.
Armaton
Member
Wonder if using a mixing valve at the storage and mixing to the minimum temperature needed for your emitters would also extend storage useability for individuals that have a WTAX in their Forced air furnace? Should aid in stratification, even if they use a P/S, since they would be using a lot of the returned water to maintain the minimum temp.
If I understand the question correctly i would think so. As mentioned, I have a Modine Hydronic Heater and one of those toe/kick heater which I believe I are simply WTAX's. They work fine for me, the blower is no much more often though - and would give the same benefit. My toe heater runs off of an aquastat so even with a low temp aquastat it will not come on in the shoulder seasons because the water temp is so low. I may require it at some point so the blower turns on whenever there is a call for heat and skip the aquastat (same as the Modine).
Thought you might be interested, I spoke to Triangle Tube yesterday and they informed me they tell people to shoot for 4 firing cycles per hour but they can live with anything under 10. There is no way to control the DeltaT so the only way to impact this is by playing with the minimum time between firing which will force a greater deltaT. The guy I spoke with was pretty knowledgeable and had a good suggestion of using the Triangle Tube to heat storage to a relatively low set point. I have an electric cutoff valve the cuts out my storage when the propane boiler fires. I can easily disengage this but I would then need to give the plumbing some thought as well as the setpoint controller which switches wood/propane heat sources according to tank temp. This would allow me to potentially get firing cycles to something like a few times per day or less. Since I rarely use propane to heat the house I will probably just stick with spreading the minimum time per fires but it is good to know should I ever tire of heating with wood and go back to propane.
maple1
Minister of Fire
I'm kind of in the dark to your scheming (lol), but I had my system plumbed & controlled so that when backup heat (electric boiler) was being used, it would only heat the distribution - it would not pull storage water. Did that with check valves. That created some pretty frequent short cycling. So this summer I pulled the check flapper out of one of my check valves & drilled a 1/4" hole in it, so that when the backup circ is running, it pulls a bit of water from bottom of storage through that 1/4" hole. That really smoothed out the electric boiler & reduced the short cycling. Of course, that means I'm paying for some kwh to heat a little bit of my storage, but I don't think it amounted to much. After a couple of days away from home over the holidays, my storage had still cooled off some, so it seemed it wasn't sending as much heat to storage as the stand by heat it was losing.
I have a modulating/condensing boiler so what they would love to see is it run at its lowest modulation for the longest period of time. So their recommendation (ideally) is to heat the tank with very low temp water (controlled by the outdoor reset) which would cause a very long low temp burn followed by a very long period pulling off of the thermal storage. My propane boiler was originally set up incorrectly plus I was heating with high temp water so, like you, I put in a check valve. One day I may revisit this for the fun of it but since I can control the short cycles via the minimum time between firing settings I will probably leave it alone until I am done tinkering with my wood setup.
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